Spectral sensitizing techniques are extremely important and necessary in preparing silver halide color photographic materials with high sensitivity and excellent color reproducibility. Various spectral sensitizing agents have conventionally been developed so as to provide high speed silver halide color photographic materials, and many techniques have been made as to their use such as supersensitizing processes, manner of adding the agents, etc.
It is known to use, as spectral sensitizing dyes for use in spectral sensitization, spectral sensitizing agents such as cyanine dyes, merocyanine dyes or complex merocyanine dyes alone or in combination (for example, for supersensitization).
Sensitizing dyes to be used in photographic materials must satisfy many requirements in addition to giving high spectral sensitivity. For example, they must not increase fog, must show good properties upon exposure (for example, latent image stability, reciprocity law properties, less dependence on temperature and humidity upon exposure, etc.), must undergo minimum change in sensitivity, gradation, and fog in shelf life and must not remain a developing solution in light-sensitive materials after development processing to avoid deterioration of white background. Sensitizing dyes for imparting red sensitivity also must meet the same requirements. However, these red-sensitizing dyes can cause serious defects for color light-sensitive materials of reduction in spectral sensitivity due to desorption of the dyes and so-called color mixing as a result of layer-to-layer transfer of desorbed sensitizing dyes, since the red-sensitizing dyes generally have a weak adsorbing power. These defects have been serious problems in practical use.
As for supersensitization, "supersensitization" is described in, for example, Photographic Science and Engineering, Vol. 13, pp. 13-17 (1969), ibid., Vol. 18, pp. 418-430 (1974), James, The Theory of the Photographic Process, 4th Ed., p. 259 (Macmillan, 1977) U.S. Pat. Nos. 3,743,510, 3,615,637, 3,674,499, 2,933,390, 2,937,039, 3,615,641, 3,635,721, 3,615,613, 3,617,295, 3,615,632, 3,649,288, 3,887,380, etc., and it is known that high sensitivity can be obtained by selecting a proper combination of a sensitizing dye and a supersensitizing agent.
However, conventional combinations of a red-sensitizing dye and a supersensitizing agent for enhancing sensitivity so as to satisfy the aforesaid requirements for light-sensitive materials seriously decrease sensitivity of light-sensitive materials particularly in shelf life, thus failing to provide sufficient properties. Although U.S. Pat. No. 3,615,632 discloses the combination of meso-substituted carbocyanine and a supersensitizing agent, the cross-linking type oxathiamethinecyanine of the present invention is not disclosed in the concrete. Further there is no description as to the improved shelf life under the condition of high temperature and/or high humidity of the present invention, in the U.S. Pat. No. 3,615,632.